LHM Limp Home Mode Experiment

20160830 Added:
Posts considered off-topic may be deleted without notice. Post repair questions elsewhere.
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I'm trying to get my head around what constitutes LHM. I know, or think I know, that there are different levels of LHM. The transmission only allowing 2nd gear and reverse operation is the most severe level. One of the questions is often whether the computer(s) have set LHM or if it is just a regular old component failure causing a regular old lack of power.

Some recent discussion got me thinking that there may be simple checks to determine if you are having a computer set LHM incident.

"Emergency Running Mode" limits to 3200 RPM. That must be "Limp-in Mode" or "Limp Home Mode" as I've seen the various descriptors used even in MB "official" publications.



So-o-o, I'd like to start an incident log in the form of this thread. It may not be the best method, but unless someone comes up with a better idea this is what we got.

Should you experience a lack of power please try raising the engine speed before you shut down the engine. If the engine will not go above about 3200 RPM, you are most likely in a computer set LHM. If the engine readily goes above that RPM you are most likely not in a LHM mode. After you determine whether you actually were in LHM or not, and you resolve your problem(s), please post what you found here.

A description of symptoms, DTC's found, etc. would be very helpful. Please don't clutter up this thread by asking questions specific to your present problems.

By the way. A problem with the Fuel Rail Pressure Sensor may limit to 2800 RPM. The difference between 2800 and 3200 RPM should be noted when doing the engine speed test.

We'll see how this thread progresses. Maybe it will just die quietly. vic

Good idea Vic!
Maybe there's some way you could turn this into a poll to make the numbers easier to capture??

mendonsy said:

Good idea Vic!
Maybe there's some way you could turn this into a poll to make the numbers easier to capture??

Click to expand...

Good idea, but with the lack of response so far I guess a poll is pointless.

I experienced my first true LHM issue recently. Any others have been set when I was messing with things.

My LHM seemed to only be that the ECM locked out the turbo vane control to limit power. I was not limited to 3200 rpm or 2800 rpm. I could climb up to over 70 mph on level highway. The problem ended up being an O2 sensor failure. Turns out the Intake Air Sensor can also cause turbo vane lockout. Both those failures may set Mass Air codes and not necessarily set DTC's specifically pointing to the failed part.

More detail can be found here:


https://sprinter-source.com/forums/showthread.php?p=161773#post161773

vic

Whoa............ before you write this off (and I think it is a GREAT idea) how about some explanation?

The way *I* read that, you wanted "current" (or future if you follow the semanitcs) experiences........ it was worded such that it sounded like you didn't want speculation or "hindsight" experiences.........

Fill us in - please!

Larry

larry8061 said:

Whoa............ before you write this off (and I think it is a GREAT idea) how about some explanation?

The way *I* read that, you wanted "current" (or future if you follow the semanitcs) experiences........ it was worded such that it sounded like you didn't want speculation or "hindsight" experiences.........

Fill us in - please!

Larry

Click to expand...

My intention is just to increase our overall group knowledge. Any input is fine. Anything is better than the nothing which my attempt has yielded so far. Post away.

Vic

Vic, this is to let you know that some of us are reading.

I couldn't get up to speed, then my wife gave me a attitude adjustment. Speed ok now.

My personal method of determining whether there is a computer set LHM.

Sometimes the computer isn't involved with low power situations. There are many levels of LHM. The test I feel applies is this:

Lower forms of LHM or Emergency Running Mode.
After having not made any repairs or alterations, if your normal operation and power returns after a simple shutdown and restart then whether you have an MIL (aka CEL) lit or not, the computer was involved in limiting the power. In most cases the symptoms will eventually return.

Additonal Info:

More severe forms of LHM.
If a shutdown/restart doesn't return operation to normal and you have a MIL (aka CEL) lit then the computer has likely set an LHM which requires clearing the codes with a scan tool (after correcting the problem).

Limited to one forward gear (likely 2nd) and reverse gear.
The most severe level of LHM. This form of LHM is often related to transmission problems. Even after the problem(s) is found and corrected, to return to normal operation this LHM generally requires reset by a scan tool capable of communication with the Transmission Control Module TCM.

As an aside. There is a computer/module response to transmission/drive train problems which doesn't allow any forward gears. I don't consider that a Limp Home Mode or Emergency Running Mode because it doesn't even let you limp.

It is not uncommon for LHM to be set with no MIL Malfunction Indicator Light aka CEL Check
Engine Light being triggered. For some faults to trigger the MIL aka CEL the fault needs to present itself twice in a row for the light to come on. A possibility is that in the case of some LHM events a key off and key on cycle negates that criteria. The fault isn't present when the key is turned back on. Then the fault returns when the engine operating conditions are such that the problem returns to again set LHM. Therefore the computer(s) never detects the fault twice in succession.

The key off cycle may need to be more than 15 seconds to allow the sequential module shutdown and the M relay to time out/de-energize.

vic

2006 2500hc 118"

Ill share my LHM experience. I had frozen actuator linkage, so the turbo was not working. I drove down the road with all the power of a ford pinto. In this condition the pinto was able to get above 60 miles an hour and although performance was incredibly poor, there was response in the pedal. Not long into driving, the check engine light came on. Now things get real bad. As you press down on the accelerator, you get almost no response, especially if you depress it 3/4. At 3/4 there is NO response. It truly feels like the computer has taken over. I couldn't get the van to go over 60. Cleared the codes and back to pinto mode. After the actuator linkage was unfrozen, all above symptoms disappeared.

I hope this helps.

Whatever happened to the guy touring South America that didn't want to believe he was in LHM?

Mine happend just yesterday. Going up a 12% grade, 3/4 of the way to the top it suddenly drops down to 2 gear with no power. I made it to the top then coast down th other side. At the bottom I step on the accelerator goes to the floor and nothing.Rmp wont go above 3200. I manualy shift it from 2nd up thru 4th which helped get me going from stop signs and up to 60 mph but acting very sluggish. Limp 50 miles to closet dealer, I called ahead and told of my problem, they had a service tech. waiting when I pulled in. Found the air temp. sensor was faulty, replaced and reset codes all was fine.I never got a warning light or nothing just out of the blue it died. This is a little concerning with only 26000 miles on vehicle, already had to replace the EGR valve at 20000 miles. Just not sure of the reliabilty of my sprinter.

Thanks, but what year and model? vic

Add your vehicle info to all your posts automatically!!!!! It's easy to do. It will help you to get answers. Thank you.

Here's how to do it.

The most direct method is probably in your "Details".
After you are logged in click on "Private Messages" (or “Quick Links”) in the upper right corner.
On the left side under "Your Profile" click on "Edit your Details".
Scroll down to the "Custom User Title" box.
Click in that box and type the information.
I suggest “Vehicle year – NAFTA or 311, etc.” depending upon your location.
Scroll down to the "Save Changes" box. Click on that and you are done.

Another place is in your "Signature".
Click on "Private Messages" (or “Quick Links”) in the upper right.
On the left look for "Setting and Options".
Click on "Edit Signature".
Scroll down to the text box which looks like what you use to add a post to the forum. Type in the information you want.
I used “NAFTA 2004 OM647 140 2500 Std Roof >246,000 mi. DAD” [/QUOTE]
Scroll down to "Preview Signature". If the preview looks like what you want, scroll down to "Save Signature", click on that and you're done.

twisted bit said:

Mine happend just yesterday. Going up a 12% grade, 3/4 of the way to the top it suddenly drops down to 2 gear with no power. I made it to the top then coast down th other side. At the bottom I step on the accelerator goes to the floor and nothing.Rmp wont go above 3200. I manualy shift it from 2nd up thru 4th which helped get me going from stop signs and up to 60 mph but acting very sluggish. Limp 50 miles to closet dealer, I called ahead and told of my problem, they had a service tech. waiting when I pulled in. Found the air temp. sensor was faulty, replaced and reset codes all was fine.I never got a warning light or nothing just out of the blue it died. This is a little concerning with only 26000 miles on vehicle, already had to replace the EGR valve at 20000 miles. Just not sure of the reliabilty of my sprinter.

Click to expand...

twisted said:

I manualy shift it from 2nd up thru 4th

Click to expand...

If you can shift into any gear other than 2nd, you are NOT in true "limp home mode".

Found the air temp. sensor was faulty, replaced and reset codes all was fine.

Click to expand...

I was going to guess "IAT" (Intake Air Temp), since mine died 3 times ... once 300 miles into new ownership (Dec 2005), once 1 year later, and once more 1 year after that.
The replacements each had a different part number, so that hints that MB knew there was a problem and kept trying new components until one worked.
The IAT sensor can drift over time (as it heads towards failure), so a ScanGauge (or similar) lets you see it coming (or can relieve you when it does).
My last one was reading 145F when it should'a said 40F .. that was just enough to tickle the CEL, but not enough for "crippled" performance.

--dick (the last change-out has now lasted 5 years, and it's only a $30 part)
(a chunk of plastic holding a single $7 (if available in the US, which it's not) Siemens thermoresistor ... which should read 6000 ohms at 68F)

autostaretx said:

If you can shift into any gear other than 2nd, you are NOT in true "limp home mode".
...

Click to expand...

You just will not give up on this one will you.

There are levels of Limp Home Mode or Emergency Running.

Here's two which are specifically mentioned.




From the above information.

"In emergency running mode. the engine speed is limited to 3200 rpm BY THE ECM. A fuel rail pressure sensor failure LIMITS the engine speed to 2800."

I see the ECM being involved in power limiting. I see "emergency running mode" LHM. Nowhere do I see any mention of transmission shifting being limited.


And one to help explain our LHM and boost problems is here.



NOTE:
"If there are faults in the boost pressure control system, the full load injected quantity is also reduced [by the ECM]."

So when there is a boost control related problem (hose leak, sensor problem, turbo, etc.) the RPM's aren't limited, BUT the full load is. That explains "can't go up hills", "no power, but on the flat I can get to 70 mph". A different form of LHM, but it is still an LHM power reduction set by the ECM.

Still not enough documentation?

Page 4 line 6 in a Mercedes specific publication.

"6. Emergency running (Limp home mode)"
Edit:
Don't bother to click the link. Yet again, a great reference has gone away. I need to remember to actually download these things so they're not lost.

http://www.mercedestechstore.com/pd...t 11 Electronic Accelerator(WJB) 04-01-01.pdf
The link went dead. I should have attached the PDF.
Search using "Systems II/508 HO Part 11 Electronic Accelerator(WJB)".
https://www.scribd.com/document/194488062/508-HO-Part-11-Electronic-Accelerator-WJB-04-01-01

I still stand by this previous post indicating levels of LHM.

Aqua Puttana said:

My personal method of determining whether there is a computer set LHM.

Sometimes the computer isn't involved with low power situations. There are many levels of LHM. The test I feel applies is this:

Lower forms of LHM or Emergency Running Mode.
After having not made any repairs or alterations, if your normal operation and power returns after a simple shutdown and restart then whether you have an MIL (aka CEL) lit or not, the computer was involved in limiting the power. In most cases the symptoms will eventually return.

Additonal Info:

More severe forms of LHM.
If a shutdown/restart doesn't return operation to normal and you have a MIL (aka CEL) lit then the computer is likely set an LHM which requires (correcting the problem) clearing the codes with a scan tool.

Limited to one forward gear (likely 2nd) and reverse gear.
The most severe level of LHM. This form of LHM is often related to transmission problems. Even after the problem(s) is found and corrected, to return to normal operation this LHM generally requires reset by a scan tool capable of communication with the Transmission Control Module TCM.

As an aside. There is a computer/module response to transmission/drive train problems which doesn't allow any forward gears. I don't consider that a Limp Home Mode or Emergency Running Mode because it doesn't even let you limp.

It is not uncommon for LHM to be set with no MIL Malfunction Indicator Light aka CEL Check
Engine Light being triggered. For some faults to trigger the MIL aka CEL the fault needs to present itself twice in a row for the light to come on. A possibility is that in the case of some LHM events a key off and key on cycle negates that criteria. The fault isn't present when the key is turned back on. Then the fault returns when the engine operating conditions are such that the problem returns to again set LHM. Therefore the computer(s) never detects the fault twice in succession.

vic

Click to expand...

Not that it really matters. Your engine operation is what it is. When it goes wrong it needs to be corrected. vic

I believe there is another degree of computer limp: 100% engine shutdown. I don't know if it's relative here, but I have experienced it (and no dealer or mechanic could ever figure it out). My van started right back up and runs fine, like it never happened. But at the time I got Christmas lights on the dash, and the engine was automatically put into neutral (going 60mph) and shut down.

There is another mode I've experienced, which is primarily a speed governed mode, with turbo turned off. Limits power to ~1/3 normal engine output (guess) and about 50mph max.

Aqua P,
Thanks for the prod to get a handle on LHM specifics.

Been a while, about 2 years, and I don't have good rpm numbers... BUT:
1) Had CEL in the mountains (Glacier NP).
2) Big mistake...had a check at a Montana "do-all" shop after going 500 miles towards home. They said it was heatex sensor & EGR issue and charged $300 (dumb me).
3) Traveled another 500 miles to Denver area and then my Sprinter went into LHM. Low rpm ( could have been less than 2800), low power and about 50mph max.
4) Waited 4 days at kids place in CO to get an appt at MB dealer outside Denver.
5) Was under warranty...no charge for an all day ERG valve replacement and heat exchanger cleaning (probably costing big bucks).
6) Since then, have put on 15,000 more miles and are now out of warranty...and am worried about next time when EGR cost will be mine.

Question...Since MB woun't pay for emissions work any more, why can't I control engine condition(LHM)?

I believe LHM should end at warranty!!!

Rock said:

Question...Since MB woun't pay for emissions work any more, why can't I control engine condition(LHM)?

I believe LHM should end at warranty!!!

Click to expand...

You do realize that would severely screw up MB's overpriced service gravy train!

My issue of LHM:

It wont allow me to get out of 2nd gear. No limits to RPMs. Drives anywhere between 20mph-35mph. Mainly 20mpg. The codes that popped up are a right rear speed sensor and a plausibility code that came up for the Mass Air Flow Sensor.

Nothing came up for the transmission. Reading the previous posts, it looks like my LMH is the more severe and its related to the transmission.

Any one have any experience with this???

First let me extend you a hale and hearty welcome to the forum.

Please start your own thread or tag onto another thread which is intended for resolving LHM problems.

The intent of this thread is for people to add their experience as to symptoms related to RPM and specific symptoms which help to identify LHM. It may have dubious value, but it will have even less if we get off on people's specific repair attempts. Thanks. vic

Edit: New thread is here.
https://sprinter-source.com/forums/showthread.php?t=24619

Sprinter2003 said:

My issue of LHM:

It wont allow me to get out of 2nd gear. No limits to RPMs. Drives anywhere between 20mph-35mph. Mainly 20mpg. The codes that popped up are a right rear speed sensor and a plausibility code that came up for the Mass Air Flow Sensor.

Nothing came up for the transmission. Reading the previous posts, it looks like my LMH is the more severe and its related to the transmission.

Any one have any experience with this???

Click to expand...

I don't know if pointing to this recent thread is in keeping with my intent for starting this thread, but there are some comments in a few posts as to rpm limits.

https://sprinter-source.com/forums/showthread.php?t=29113

vic

If You have a Sprinter capable ODBII unit (like a DAD) you can read the transmission error codes. If you have only a generic ODBII reader, you won't be able to access the transmission codes. You have an issue with the TCM limiting your shifting - it could be from a lot of things. Get the transmission codes read.